Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Common stock, par value	$ 0.625	$ 0.625
Common stock, shares authorized	120,000,000	120,000,000
Common stock, shares issued	67,254,859	67,083,149
Common stock, shares outstanding	37,701,950	37,895,641
Treasury stock, shares outstanding	29,552,909	29,187,508